Variable resistor constructions



April 22, 1958 M. E. BOURNS 2,831,949

VARIABLE RESISTOR CONSTRUCTIONS Filed May 5, 1954 2O -SO LH 32 37 O O A4 (I7 f /h f'4 im\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\Wmi Mmmmem 1N VENTOR MARLAN E. BOURNS ATTORNEY 2,831,949 y VARIABLE RESISTOR CONSTRUCTIONS Marlan E. Bourns, Riverside, Calif. y y

Application May 3, 1954, `Serial No. 427,326 y 2 Claims. (Cl. 201-62) and improved producing better variable resistors of a small size atv a` comparatively low cost have ceased.

It is an object ofthe present disclosure to teach the production of new and improved variable resistors which are more acceptable than the prior units` designed to accomplish the same results by one or Vmore of the criteria indicated1 above. More specifically, it is an object of the present invention to provide potentiometer and rheostat constructions which are 'dependable,small` and compact, and comparatively simple to manufacture. Further objects of the present invention, as well as the advantages ofV it, will be apparent from the balance of this specilication,'the appended claims and the accompanying drawings inl which: y

Figure l is aside view of a variable resistor of the invention;

Figure 2 is a cross-sectional view taken at line 2-2 of Figure l;

Figure 3 is a` cross-sectional view taken at line 33 of Figure2; y

Figure 4 is a partial cross-sectional View taken at line 4 4 of Figure 2;

Figure 5 is another partial cross-sectional view taken at line 5 5 of Figure 2'; n

Figure 6 is an isometric view of a slider employed in the construction of Figure l; t

vFigure 7y is an isometric view of a contact member which iscarried by the slider shown in Figurey 6;

Figure 8 is a cross-sectional Viewv similar to Figure, 3

of a modified variable resistor construction of the in-` vention;

Figure 9 is a cross-sectional View similar to Figure 3 of a second modified variable resistor construction of the invention; and

Figure 10. is a partial crosssectional view taken at line 10-10 of Figure 9.

Figure ll shows a detail of the terminal connection" of Figure 3.

- UnitedStates Patent() 2,831,949 Patented Apr. 22, 1958 ICC cover and said at upper surface, spring contact means carried by said slider, means mounted for moving said slider and said spring contact member with respect to said upper surface so that said spring contact member is in constant engagement with said electrically conductive members and terminal means projecting through said base member and being in electrical contact with said electrically conductive members.

More specifically it may be stated that this disclosure is concerned with potentiometer or rheostat constructions of the broad category indicated in the preceding paragraph in which a large number of structural innovations are employed to produce electrical components of the class described which are relatively inexpensive and easy to manufacture, which are comparatively small and compact and which are extremely dependable in operation. It is thought that the nature of these structural details will be best more fully explained by referencek to the drawings accompanying this application. T he various tigures of the drawings, are not necessarily drawn to scale, but are drawn in order to conveniently illustrate the details of the present invention.

Referring now to Figure l through 5 of` the drawings, where itis seen that a variable resistor 10 of the invention includes a base 11 of an insulating material such as a lled phenol-formaldehyde resin having a substantially flat upper surface 12, and upstanding ends 14. The sides 15 of the base 11 are provided with` notches 16 which lead past the ends of the upper surface 12 into the upstanding ends 14h4 Within these ends the notches 15 intersect with vertical notches 17. With this construction itis thus possible for sides 19 of a cover 20 formed of metal to be placed along the base 11 between the upstanding ends 14. These sides 19 are connectedv to a top 21 posiytioned generally parallel to the at upper surface 12 between the ends 14 of the base 11. This top 21 is adapted i to generally overlie the ends 14, and is adapted to be se- In all gures of the drawings like numerals are used to y designated like parts.

The present disclosure may be brieily summarized as being concerned with variable resistor constructionsk including a base member having a relatively flatupper surface, a cover positioned over said base` member so as to be spaced generally from saidflatupper surface, electrically conductive members disposed parallel to one another. uponfsaid upper surface, kat least one of said electrically conductive members being of appreciable electrical .resistancev characteristics, a slider mounted between said cured to these ends by means of fastening arms 22 attached to the top 21 adjacent to the endsy14 so as to lie within notches 23. Each of these notches 23 is intersected adjacent to the bottom 24 of the base 11 by another notch 25. The fastening arms 22 include dependent projections 26 which are designed to lit within these notches 25.

Normally sides 19, the arms 22 and the projections 26 i are formed in such a manner that they grasp the base 11 with a spring-like or snap action preventing undesired displacement of the cover 20 with respect to this base 11. In order to securek a spring-like action of this category the cover 20 `is preferably formed of a resilient metal. If desired auxiliary means such as eyelets passing through the sides 19 and the ends 14 can be utilized to position the cover 20 with respect to the base 11. When such means are employed it is not necessary to utilize fastening arms such as the arms 22.

The upper surface 12 of the base 11 is provided with a substantially square-shaped notch 30 which is adapted to hold an inverted U-shaped conductor 31, which serves as an electrical return means from the resistance element to a terminal, the sides of said conductor being urged against the sides of the notch 30 by means of the inherentresiliency of the material from which the conductor 31 is manufactured. Suitable materials for this purpose include Phosphor bronze, copper, etc. One side of the conductor 31 is formed with a projecting terminal tab 32 which is adapted to lie within an opening 33 connecting the bottom 24 of the base11 with the notch 30. With this construction the tab 32 is securely held with respect to the rest of the variable resistor 10.

The upper surface 12 ofthe base 11 is also provided with a notch 34 which is adapted to hold an insulating rcore 35) uponA whi'chthere has been placed ay spiral resistance element 36. This resistance element 36 is normally held in place by means of terminal tabs 37 projecting through apertures 33 connecting the upper surface 12 and the bottom 24 of -the base 11. These tabsV 37 are preferably formed ina bent configuration 39 so that they are held within the apertures 38 adjacent theV element 36 by spring tension. The tabs 37 may, if desired, be formed in specialized shapes corresponding to the shape of the resistance element 36 so as to aid in retaining this resistance element within the notch 34, or, if desired, may be cemented in position in addition to being held by spring tension. lf desired the resistance element 36 can be pressed within this notch so as to beheld in position by a force-fit type of action. rThe resistance element can also be held in positionl by various adhesives. lf any portion of the resistance element adjacent to the tabs 37 isf covered with an insulating coating this coating is, of course, removed before or during .the assembly of the final device so as to establish electrical contact.

`Between the cover 2t) and the base 11 there is disposed a slider 40 formed of an insulating material such as a lled phenol-formaldehyde resin, such as is shown in Figure 6 of the drawings. This slider is designed to fit between the vwalls 19 and is provided with an internal threaded bore il and edge slots 42. These edge slotsare adapted to carry curved projecting ears 43 of a spring member 44 of Phosphor bronze, stainless steel or the like such as is specifically shown in Figure 7. This spring member 44 also includes dependent curved contact mem-- When these ears 43 are held within the slots 42 bers 45. of the slider 40 there is substantially no danger of the spring member 44 moving away from the slider 40; and the contact members 45 are spaced from the bottom of the slider 40. As is apparent from the drawings, the spring member 44 doesnot project beyond the confines of the slot Li2 toward the walls 19 or the top 21 and is thus at all times insulated from these walls and this top.

The slider et) is normally held in position with the contact members 45 being disposed against the upper most portions of the U-shaped conductor 31 and the resistance element 36 by means of a shaft 50 having a threaded section 51 and smooth ends 52 and 53. The end 52 is normally located within a cavity 54 located in one of the ends 14; the other end 53 normally projects from the variable resistor through a notch 56 formed in the other end 14; and the threaded section 51 carries the slider di). The end 53 is adapted to be held in position within the notch 56 by edge projections 57 formed on the end 14 within the notch 56 and by means of a similar projection 58 formed on the top 21 of the cover engaging a shoulder which may conveniently be provided by a circumferential groove 55 in the shaft 50. A projection 59 formed on the top 21 of the cover 2'3 is adapted to bear against the end 52 of the shaft 5t). Both of these projections 58 and S9 are effective because of the inherent resiliency of the material from which they are made in controlling the tension on the shaft Si) so that all times a uniform amount of force is required to turn this shaft. These projections also serve to ground the shaft 50 to the cover 2i). With the specific construction shown the slider 4f) and the contact member d4 can be moved by rotating the shaft 50 so that the spring contacts 4S are placed in position against desired adjacent portions of the conductor 31 and the resistance clement 36. Rotation of the slider 40 when the shaft 50 is rotated is prevented by projections or runners 63 extending downwardly from the side of the slider 40 adjacent to the base 11 and slidably engaging the exposed sides of the conductor 31. If desired such projections or lugs may be formed elsewhere on the slider 40 in order to engage other portions of the resistor 10 in order to accomplish the same result.

The modified construction shownin Figure S of the drawings differs from that shown in Figures 1 through 6 in that the conductor 31 and the resistance element 36 are replaced by a metal strip 64 and a parallel resistance member 60 disposed within slots 61 formed in the base 11. Any electrically conductive metal, such as, for example Phosphor bronze, copper, etc. can be used for the strip 59; and the member 60 can be formed of a suitable resinous resistance composition. Suitable compositions are known to the art and include mixtures of carbon black and phenolic resins. The construction shown in Figure 8 also differs from that of Figure 3 in that the terminal tabs 32 and 37 are replaced by terminal tabs 62 wedged within apertures 63' in the base 11 connecting the upper surface 12 with the bottom 24. The tabs 62 include bent over spring contact portions lying generally parallel to the upper surface 12 making'contact with the upper surface of the strip 59 and the resistance member 60. With this specific construction the tab employed with the strip 59 is located adjacent to the end of this strip sopas not to interfere with the movement of the slider 40.

In Figure 9 there is shown another modified construction which differs from the preceding variable resistors in that terminal tabs 65 are employed which are molded within the base 11 so as to project from both the upper surface 12 and the bottom 24. These tabs 65 are adapted to be secured to resistance films 66 positioned upon supporting insulating bases 67 dispersed within slots 68 by means of solder 69. These resistance films 66 can be of any resistance composition known to the art of producing printed circuit components; if desired these resistance films 66 canbe placed directly upon the upper surface 12 of base 11. The construction shown in this figure is primarily designed to be employed as a rheostat. In order to prevent interference with the movement of the slider 40, the tabs 65 are preferably located adjacent to the ends of the resistance films 66. If desired a silver ink l-or other highly conductive film can be substituted indicated in that the bore 41 is not threaded and in that there is provided an internal cavity 71 which projects into the center portion of the slider 40 so as to be intersected in the bore 41 from adjacent to the top 21 of the cover 20. Disposed within the cavity 71 is a follower 72 formed of a resilient metal having sides 73 and 74 joined at an apex 75. Both of these sides 73 and 74 are provided with side openings 76 and 77 respectively which are of such a dimension that as the sides 73 and 74 are pulled together the shaft 50 may be readily inserted within the openings 76 and 77 without threading the shaft 50 through such a dimension that once the shaft 50 and the follower 72 are positioned substantially as located the sides 73 and 74 may be released so as to allow at least part of one of these two openings to fit within the threads on the section51 of the shaft 50. When the sides 73 and 74 have been released in this manner they engage edges 78 of the cavity 71 so as to wedge the follower 72 against the slider 40 in such a manner that as the shaft 50 is turned the slider 40 will be moved. This construction has the advantage of substantially eliminating backlash.

Both of the sides 73 and 74 terminate in bentover end sections 79 which engage the top 21 0f the cover 20 on the side of the slider 40 remote from the spring member 44. These bentover end sections 79 are designed to exert a spring action .upon the top 21 which will tend to prevent rotation of the slider 40 when the shaft 50 is rotated. ln order to achieve this purpose the amount of force required to deform these ends 79 must be greater than the amount of force required to bend the curved contact members 45.

various conductive and resistance means shown can be substituted for one another although they are not to be considered as complete equivalents. Similarly the follower arrangement shown in Figure can be substituted for the projections shown in Figure 3 and Figure 4, and

such projections can be used in place of this follower arrangement in the construction of Figure l0, although these items are not strictly equivalents. Further, resistance films such as a metal resinate film on a cylindrical supporting surface can be substituted for the resistance element 36. It is also possible to form the tabs 32, 37, 62 and 65 in the form of plugs designed to t mating sockets. All such modifications of this category are to be considered as part of the invention insofar as they are dened by the appended claims.

It is believed that the specilic advantages of the various constructions indicated in this specification will be so obvious to those skilled in the art that it will be unnecessary to discuss them in detail. Constructions as herein shown and described can be manufactured comparatively cheaply, using a minimum number of parts and constitute a major improvement over the prior devices of a similar category presently being manufactured for this reason. Another major advantage of the invention lies in the fact that a wide variety of different resistance or conductive films can be utilized as desired in order to obtain any desired results. The terminal tabs illustrated can be easily formed in such a manner that they can be utilized in mounting the units of the invention.

I claim:

1. A device of the class described, comprising ya body, an electrically conductive element mounted on said body, a slider positioned above said element and movable along the length thereof, a rotatable lead screw extending through said slider and having threaded engagement therewith, a pair of laterally spaced projections extending downwardly from the underneath side of said slider and engaging said device on opposite sides of said element, to prevent said slider from rotating with said lead screw, and a contact carried by said slider, said contact v engaging said electrically conductive element.

f 2. A variable resistor rcomprising a body, an elongated kresistance element mounted on said body, a conductor strip mounted on said body alongside said resistance element, a slider positioned above said resistance element References Cited in the le of this patent UNITED STATES PATENTS 1,080,230 Purssell Dec. 2, 1913 1,371,049 Oler Mar. 8, 1921 1,460,239 Gehrig June 26, 1923 1,621,233 Campbell Mar. 15, 1927 1,692,962 Thompson Nov. 27, 1928 1,839,343 Sachse Jan. 5, 1932 1,947,828 Codney Feb. 20, 1934 2,020,289 Bullinger Nov. 12, 1935 2,115,135 Benbow Apr. 26, 1938 2,204,086 Kamenarovic June 11, 1940 2,229,072 Green Jan. 21, 1941 2,242,327 Rubinstein May 20, 1941 2,443,020 Beier lune 8, 2,485,464 Stott Oct. 18, 1949 2,506,482 Batcheller May 2, 1950 2,625,633 Warsher Jan. 13, 1953 2,668,218 Searle Feb. 2, 1954 2,687,463 Riley Aug. 24, 1954 2,718,577 Sherk Sept. 20, 1955 

